Cisco 2900XL series problems

[mmcgurty]

I was wondering if anyone else has had this issue. Recently we purchased a mass quantity of Dell GX620 towers. When we plug them into a Cisco WS-C2950-24, they seem to autonegotiate just fine. However, when plugging into a Cisco WS-C2924-XL-A or WS-C2924-XL-EN the port will go through STP processes, go green, then start over as if you unplugged it and plugged it back in. The Dell GX620 uses a Broadcom 5751 10/100/1000 network interface card built into the system. When we set "spanning-tree portfast" on the 2900XL switch ports, they work just fine. We are using Windows 2000 Workstation, SP4. Anyone have any idea why the 2900XL's would do this?

 

[ADB100]

I assume the 2950's have already been configured for STP portfast. With the 2950 you can globally enable STP portfast so it doesn't actually show in the configuration of the port but appears in global config:

!global
spanning-tree portfast default
!
interface FastEthernet0/4
switchport access vlan 10
!

There isn't the equivilent command for the 2900XL series and STP portfast must be configured separately on each port.

It could also be the STP mode of the 2950 has been changed to Rapid-PVST or MST instead of the defaul PVST. With Rapid Spanning Tree access ports will begin forwarding much quicker than when running 802.1d STP. The 2900XL only supports PVST.

HTH

Andy

 

[mmcgurty]

No, the Cisco 2950's have not been globally nor individually configured for spanning-tree portfast. I suspect it may be a case of the PVST support. I checked one of the Cisco 2950's and it showed this "spanning-tree mode pvst". I appreciate the information thus far, that might be something for me to go on.

 

[ADB100]

The default STP mode for both the 2900XL and the 2950 is PVST (Per VLAN Spanning Tree), if the switches are pretty much default each port will take about 45-seconds to begin forwarding traffic. There should not be a difference between the 2 switches.

Maybe post some configs (or parts of) and we can help more?

Andy

 

[vipergg]

All user ports should have spanning tree portfast turned on anyway . Only switch to switch links should not have portfast turned on .

 

[mmcgurty]

Couldn't you introduce bridge loops in your switches when you enable spanning-tree portfast on all ports but uplinks? Especially when people still plug in hubs, unmanaged switches, etc?

 

[vipergg]

If you get any it should be temporary , spanning tree is still running on the ports it just eliminates a couple of the steps so the ports come up faster . It will still block looped ports .

 

[jneiberger]

Do you have both sides of the connections set to AUTO, or just the switch side?

 

[mmcgurty]

We tried both sides set to Auto/Auto and 100/Full, thinking it might be the 1000mb adding something to the mix since we are only 100mb ports. Neither made a difference in the connection until we added "spanning-tree portfast" to the port. At first, I thought maybe it was a feature added since Gigabit was standardized. Like Flow Control or packet size options for the adapter.

 

[jneiberger]

I just wanted to make sure because the 2950 and the 2924XL handle autonegotiation a little differently. However, they will behave the same as long as you always set both sides to AUTO.